So close was he to one exclusive set of donors that he spent his birthday with a group of them last October, sharing a cake in the shape of the House of Commons.

The Conservative Party deny any impropriety on behalf of the Prime Minister. But the lobbying scene is certainly one he professes to know well.

“We all know how it works,” he said in his 2010 speech. “The lunches, the hospitality, the quiet word in your ear.”

And he knows exactly why the public will view the allegations, made by his former aide and his own party treasurer, in such a dim light.

“We don’t know who is meeting whom. We don’t know whether any favours are being exchanged. We don’t know which outside interests are wielding unhealthy influence,” he explained in the speech with now threatens to haunt him."

The venue for the speech was perhaps ironic given yesterday’s revelations.

The University of East London is less than a mile or so from where Peter Cruddas, the man whose promises of access to Mr Cameron in exchange for cash has cast a dark cloud over the Prime Minister, grew up

And it was another former resident of east London, Mr Cameron’s former aide Sarah Southern, who once lived in Bethnal Green, who set the scandal in motion by boasting to fellow lobbyists that she had made a “tidy sum” by introducing a client to her former boss.

The warning signs for the Prime Minister were evident before yesterday’s revelations.

In December last year executives at the lobbying firm Bell Pottinger were secretly recorded telling journalists that they could get access to David Cameron. The allegations led to a flat denial from Downing Street that lobbyists had any influence over the Prime Minsister.

However the Conservative Party do not deny that extravagant donations are rewarded with access to senior party figures.

The Party’s website sets out benefits of being a member of one of its 'donor clubs’. The highest echelon is 'The Leader’s Group’ which is described as “The premier support group of the Conservative Party”.

For a fee of £50,000 a year, the website explains: “Members are invited to join David Cameron and other senior figures from the Conservative Party at dinners, post-PMQ lunches, drinks receptions, election result events and important campaign launches.”

However yesterday’s allegations in the Sunday Times allege that a far cosier relationship was provided for those who made bigger donations.

The revelations were set in motion after Mark Adams, a lobbyist and former private secretary to John Major and Tony Blair, was told by Miss Southern, who now runs her own consulting firm complete with business cards featuring pictures of her with Mr Cameron, about her “tidy sum”.

He alerted the Sunday newspaper and their reporters posed as overseas financiers met with Miss Southern in a hotel overlooking Lake Zurich.

The undercover reporters claimed that their clients intended to buy distressed government assets, such as Royal Mail, and wanted to make political connections.

Miss Southern, 31, is alleged to have boasted of her connections to David Cameron, cultivated through seven years of work at the Conservative Party. “I spent more time in the first third of [2010] with DC than I did with anyone else in my life,” she said.

Miss Southern, who proposed a fee of £15,000 per month, suggested a meeting between the reporters and Mr Cruddas to discuss a “huge donation” which would gain them access to Mr Cameron.

Mr Cruddas told the reporters that a fee of £250,000 would put them in the “premier league” of businessmen who enjoy privileged access to the Prime Minister.

Mr Cruddas, the 90th richest person in Britain and the Tory party’s second largest donor, then went on to boast about the access he could provide to Mr Cameron.

He explained that donating such a large sum of money would ensure that their views were “fed in” to the policy unit at No 10. And he claimed that once they had become “part of the system” donors could be invited to Chequers.

Mr Cruddas claimed that donors’ political connections would also mean they could invite their friends and clients to parties at stately homes such as Highclare Castle, the setting for the ITV costume drama Downton Abbey.

Mr Cruddas said that other senior Tories could be accessed for the right fee. He said: “If you want important clients to be at the Cameron dinners then…we can easily get you to meet Cameron and Osborne and Hague and Gove and people like that, Theresa May.”

Mr Cruddas explained to the reporters exactly how the access could work. “If I know what your expectations are, I can manage those. And I’ll make sure if you ring me up [or] Sarah rings me up one day and says I’ve got this really important guy coming to this event, you know, really need to make sure George Osborne says hello to him, and I’ll make sure that happens...not officially, but I’ll make sure it happens.”

He added: “If you donate you will be invited to events where the Prime Minsister is there. And frequently, if you get into the right club and I can advise you, you could well be at a private house having a private dinner with the chancellor, William Hague, David Cameron, Michael Gove, all the top ministers, the chairman of the party, where around that table will be some very distinguished business people.”

And Mr Cruddas said that one wealthy donor had already used his access to express his anger about proposals to legalise gay marriage. Mr Cruddas said the donor had written a paper on the subject which had been passed to the No 10 policy unit.

He added: “We’ve fed that back into the party and there are some brilliant points in it and his voice has been heard.”

As well as filling the Party coffers, Mr Criddas told the undercover reporters that he was raising funds to defend the proposed changes to constituency boundaries, which he said could gift the party an extra 50 seats.

But he will have little chance to enact this plan. Even before the Sunday Times had hit the streets yesterday, Mr Cruddas resigned his position as co-treasurer of the Conservatives, quitting on Saturday evening just hours before publication.